The present invention relates to a new and improved method and apparatus for use in casting a metal article and more specifically to a method and apparatus which may be used in casting of a thin metal article.
Thin wall equiaxed castings are used as turbine exhaust case components in jet engines. The thin wall castings typically have a thickness of 0.020 to 0.030 inches and may be 40 to 150 square inches in size. They frequently have stiffening ribs to impart adequate rigidity and may contain threaded attachment studs, pads for bolt holes and/or end wall flanges.
Although this type of thin wall casting has been made using a lost wax process and a vacuum casting process, it has not been possible to obtain adequate dimensional control of the wall, that is control of up to plus or minus 0.005 inches. Previous attempts to make these thin wall castings have resulted in wall thicknesses of 0.015 inches or less to 0.06 inches or more. This poor dimensional control of the wall thickness of objectionable.
One known method of casting a thin walled metal article is disclosed in U.S. Pat. No. 5,623,985. This patent discloses the concept of using ceramic pins to stabilize side sections of a mold structure. The ceramic pins leave small holes in the thin wall cast article. These small holes may, in some circumstances at least, be objectionable.
The present invention provides a new and improved method and apparatus for use in casting a metal article. The apparatus includes a mold structure having one or more metal pins which extend between wall sections of the mold structure. Bent end portions of the pins are disposed in the mold wall sections. Central or connector portions of the pins are disposed in the mold cavity and extend between the mold wall sections. Force is transmitted through the pins to retard relative movement between the mold wall sections during casting of the metal article.
Although the method and apparatus of the present invention may be utilized to cast many different types of articles, it is believed that the apparatus will be particularly advantageous for forming of castings having thin wall areas. Thus, the method and apparatus may be used to cast a metal article having thin wall areas with a thickness of 0.060 inches or less. The thin wall article has a length and width of at least four inches or more. Although the metal pins may have many different dimensions, it may be preferred to use metal pins having a thickness of 0.030 inches or less.